1. Field of the Invention
The present invention relates to an image reading apparatus, and more particularly, to an image reading apparatus of a flow-reading mode by an auto original feeding in a copying machine or a scanner.
2. Description of the Related Art
Conventionally, in an image reading apparatus which optically reads an image of an original, a fixed-reading mode and a flow-reading mode are used alone or in combination. In the fixed-reading mode, an image of an original held on a platen glass is read. In the flow-reading mode, an original is conveyed one by one, and an image of the original is read during conveyance. Since the flow-reading mode can read images of a large quantity of originals by a single operation and has high productivity, the flow-reading mode is commonly used in a monochrome copying machine or a color copying machine.
In the case of the flow-reading mode, a reading optical system is focused on an image plane of an original which is conveyed over a transparent member (reading glass) such as an elongated reading glass. Therefore, it is easily affected by foreign matter such as dust adhered to or remaining on the reading glass, and a portion shielded by the foreign matter becomes a line-shaped image noise in a read image. When the original is a paper, minute foreign matter such as a filler or a fiber included in the paper, for example calcium carbonate, is adhered to the reading glass.
As a measure against the image noise, the following measures have been taken. In the process of processing the read image, the dust on the image is detected and a warning in issued to a user. Image processing is performed to remove the line-shaped noise. The reading glass is shifted such that the dust is not continuously read. However, in these measure, since dust is deposited on the reading glass, it is finally necessary for a service engineer to clean a surface of the reading glass.
Therefore, as disclosed in Japanese Patent Laid-Open No. 2010-89851, there is proposed an image reading apparatus which cleans a top surface of a reading glass by rotating an elastic cleaning member. The method of rotating the cleaning member can be operated between originals being conveyed because a cleaning time is short. Hence, the reading glass can be always kept clean. Therefore, it is effective to the reading in the flow-reading mode.
In the method of rotating the cleaning member, it is necessary to control a position of the cleaning member at the time of starting a job and ending a job, on the assumption that a state in which the cleaning member is directed in an upward direction is a home position. The control at the time of starting the job is done for shading correction. The control at the time of ending the job is done for preventing the cleaning member from being damaged by the user's touch with the cleaning member.
In Japanese Patent laid-Open No. 2010-89851, a detection of a home position of a cleaning member is performed in such a manner that a phase detection portion formed in a gear or a pulley is detected by using a sensor such as a photo interrupter. However, in this case, a space for mounting the sensor is needed, which is disadvantageous to compactification of an apparatus. Also, in the case of using the sensor, it is necessary to consider a phase focusing between a cleaning member and a driving unit at the time of assembling, which is disadvantageous to an assembling property and a maintenance property.
Therefore, it is desirable to provide an image reading apparatus which detects a home position of a cleaning member without using sensors, so that the image reading apparatus can be compact and inexpensive and can improve an assembling property and a maintenance property.